1. Technical Field
The present invention relates generally to an automatic transmission and more particularly to a method of determining the shift lever position selected by the driver of a transmission that is controlled electronically and hydraulically.
2. Discussion
Generally speaking, land vehicles require three basic components. These components comprise a power plant (such as an internal combustion engine) a power train and wheels. The internal combustion engine produces force by the conversion of the chemical energy in a liquid fuel into the mechanical energy of motion (kinetic energy). The function of the power train is to transmit this resultant force to the wheels to provide movement of the vehicle.
The power train's main component is typically referred to as the "transmission". Engine torque and speed are converted in the transmission in accordance with the tractive-power demand of the vehicle. The vehicle's transmission is also capable of controlling the direction of rotation being applied to the wheels so that the vehicle may be driven both forward and backward.
A conventional transmission includes a hydrodynamic torque converter to transfer engine torque from the engine crankshaft to a rotatable input member of the transmission through fluid-flow forces. The transmission also includes frictional units which couple the rotating input member to one or more members of a planetary gearset. Other frictional units, typically referred to as brakes, hold members of the planetary gearset stationary during flow of power. These frictional units are usually brake clutch assemblies or band brakes. The drive clutch assemblies can couple the rotating input member of the transmission to the desired elements of the planetary gearsets, while the brakes hold elements of these gearsets stationary. Such transmission systems also typically provide for one or more planetary gearsets in order to provide various ratios of torque and to ensure that the available torque and the respective tractive power demand are matched to each other.
Transmissions are generally referred to as manually actuated or automatic transmissions. Manual transmissions generally include mechanical mechanisms for coupling rotating gears to produce different ratio outputs to the drive wheels. Automatic transmissions are designed to take automatic control of the frictional units, gear ratio selection and gear shifting. A thorough description of general automatic transmission design principals may be found in "Fundamentals of Automatic Transmissions and Transaxles," Chrysler Corporation Training Manual No. TM-508A. Additional descriptions of automatic transmissions may be found in U.S. Pat. No. 3,631,744, entitled "Hydromatic Transmission," issued Jan. 4, 1972 to Blomquist, et al., and U.S. Pat. No. 4,289,048, entitled "Lock-up System for Torque Converter," issued on Sept. 15, 1981 to Mikel, et al. Each of these patents is hereby incorporated by reference.
In general, the major components featured in such an automatic transmission are: a torque converter as above-mentioned; fluid pressure-operated multi-plate drive or brake clutches and/or brake bands which are connected to the individual elements of the planetary gearsets in order to perform gear shifts without interrupting the tractive power; one-way clutches in conjunction with the frictional units for optimization of power shifts; and transmission controls such as valves for applying and releasing elements to shift the gears, for enabling power shifting, and for choosing the proper gear, dependent on shift-program selection by the driver, accelerator position, the engine condition and vehicle speed.
The control system of the automatic transmission is typically hydraulically operated through several valves which are operable for directing and regulating the supply of pressurized fluid. This hydraulic pressure control will cause either the actuation or deactuation of the respective frictional units for effecting gear changes in the transmission. The valves used in the hydraulic control circuit typically comprise spring-biased spool valves, spring-biased accumulators and ball check valves. Since many of these valves rely upon springs to provide a predetermined amount of force, it will be appreciated that each transmission design represents a finely tuned arrangement of interdependent valve components. While this type of transmission control system has worked well over the years, it does have its limitations.
In view of these limitations, several advanced transmission control systems have been proposed. One such system was disclosed in U.S. Pat. No. 3,956,947 to Leising, et al., issued on May 18, 1979, the disclosure of which is hereby incorporated by reference. The automatic transmission disclosed in U.S. Pat. No. 3,956,947 features an adaptive control system that includes electronically operated solenoid-actuated valves for controlling certain fluid pressures. In accordance with this electric/hydraulic control system, the automatic transmission would be responsive to an acceleration factor for controlling the output torque of the transmission during a shift from one ratio of rotation (between the input and output shafts of the transmission) to another. Specifically, the operation of the solenoid-actuated valves would cause a rotational speed versus time curve of a sensed rotational component of the transmission to substantially follow along a predetermined path during shifting.
Another advanced transmission control system was disclosed in U.S. Pat. No. 4,965,735 to Holbrook et al., the disclosure of which is hereby incorporated by reference. The system disclosed in U.S. Pat. No. 4,965,735 in an improved adaptive transmission control system utilizes an electronic controller to receive input signals indicative of engine speed, turbine speed, output speed (vehicle speed), throttle angle position, brake application, predetermined hydraulic pressure, the driver selected gear, engine coolant temperature and/or ambient air temperature. The controller generates command signals for causing the actuation of a plurality of solenoid-actuated valves which regulate the application and release of pressure to and from the frictional elements of the transmission system. Accordingly, the controller executes predetermined shift schedules stored in the memory of the controller through appropriate command signals to the solenoid-actuated valves and the feedback which is provided by various input signals.
Another significant aspect of U.S. Pat. No. 4,965,735 is the ability to utilize closed-loop feedback to control the transmission. Closed-loop feedback allows the control system to perform its functions based on real-time feedback sensor information. This is particularly advantageous as the control actuation can be corrected as opposed to an open-loop control in which signals to various elements are processed in accordance to a predetermined program. The controller is also programmed to determine the shift lever position of the driver selected gear of the transmission to provide hysteresis between the various gear positions, and to provide limited operation of the transmission in the event the sensors which determine the driver selected gear or operating conditions are not operating properly.
Despite these advancements, there remains a need in the art for an improved transmission control system which is more reliable in operation and which provides improved fault detection. Furthermore, there remains a need in the art for an improved transmission control system which provides enhanced functionality despite the existence of a fault within the transmission control system.